Facilities in which hazardous materials are handled threaten the safety of workers during maintenance work. In the case of a gas leak accident that occurred in Gumi on Sep. 27, 2012, a worker accidentally opened a tank valve while the worker was injecting hydrofluoric acid gas into a facility, and thus a gas leak occurred, resulting in the deaths of five workers and injuries to eighteen workers.
In the case of such hazardous facilities, it is now common for other workers to keep watch while a worker is working, so as to prevent a facility from being operated, or a worker begins working after manually stopping the operation of the facility. However, there is always a risk because the access of other workers cannot be fundamentally blocked, and mistakes of workers cannot be blocked. The problem is more serious because a momentary mistake may lead to loss of lives.
Information disclosed in this Background section was already known to the inventors before achieving the present invention or is technical information acquired in the process of achieving the present invention. Therefore, it may contain information that does not form the prior art that is already known to the public in this country.